In creating a fluid filter, an attempt is made to maximize the loading capacity while simultaneously minimizing the volume of the filter itself and its face velocity. Simultaneously, it is desirable to simplify or eliminate the housing structure necessary to support the filter. All of these factors must be considered with an eye to keeping the overall cost to a minimum.
Pleated paper filters with rigid housings have long been the industry standard for most filtering application. These filters, however, require relatively expensive housing structures and have relatively low filter densities and loading capacities.
Attempts have been made to increase the filter density and loading capacity of filter elements. One such filter is described in U.S. Pat. No. 2,322,548 issued to Sigmund wherein an impervious board matrix separates a flat filtering sheet which is rolled into a cylindrical shape. Filtering occurs when the fluid entering the intake side must cross through the inner walls at a right angle to exit by the outlet side. U.S. Pat. No. 2,210,397 issued to Dreiss uses a similar to orthogonal flow filtering scheme by carefully aligning two sheets of substantially flat filter paper with a specially designed top and bottom plates to direct airflow. U.S. Pat. No. 3,020,977 issued to Huppke et al introduces the additional feature of corrugated material between flat sheets, although the corrugated material performs no filtering function, merely acts as a spacer. Likewise, U.S. Pat. No. 2,397,759 issued to Sigmund employs a corrugated member as a spacer. None of these devices is able to achieve the high filtering density desired because of the use of materials which are merely structure rather than both structural and performing a filtering function.
The present invention recognizes the value of orthogonal filtering flow while insuring that every element of the filter performs both a structural and a filtering function, rather than merely one or the other. Thus, the desired result of maximizing strength and filter density while reducing face velocity and cost are achieved by the present invention.